1. Field of the Invention
The present invention relates to a lithography simulation method, a mask pattern preparation method, a semiconductor device manufacturing method and recording medium.
2. Related Background Art
In recent years, a semiconductor manufacturing technology has advanced very remarkably, and with rapid progresses of micro pattern forming technologies such as a mask process technology, a photolithography technology and an etching technology, a semiconductor device having a minimum working size of 0.13 μm is nowadays produced in large quantities.
In the days when a pattern size is sufficiently large, a planar shape of an LSI pattern to be formed on the wafer is drawn as a design pattern without modification to prepare a mask pattern faithfully to the design pattern. Then, the mask pattern is transferred onto the wafer by a projection optical system, and an underlayer is etched, whereby the pattern can be formed on the wafer substantially as designed. However, as the miniaturization of the pattern advances, it becomes difficult to form the pattern faithfully in each process, and a problem occurs that a final finishing dimension is not faithful to the design pattern.
To solve the problems, processing (hereinafter referred to as the mask data processing) becomes very important which prepares the mask pattern that is different from the design pattern in consideration of a conversion difference between the processes so that the final finishing dimension becomes equal to a design pattern dimension.
The mask data processing includes OPC processing to correct an optical proximity effect (OPE) and the like in addition to processing to change the mask pattern by use of graphic calculation processing, a design rule checker (D.R.C.) and the like, and the mask pattern is appropriately corrected by these processings so that the final finishing dimension becomes a desired dimension. In recent years, with further miniaturization of a device pattern, a K1 value (K1=W/(NA/λ), wherein W: dimension of the design pattern, λ: exposure wavelength of an exposure apparatus and NA: numerical aperture of a lens for use in the exposure apparatus) in a lithography process is increasingly reduced. As a result, since the OPE tends to further enhance, a load of optical proximity correction (OPC) processing becomes very large. To achieve a high precision of the OPC processing, a mainstream is a model base OPC technique which can calculate an appropriate correction value for each mask pattern by use of a light intensity simulator capable of correctly estimating the OPE.
To perform high-precision correction by the model base OPC, a high-precision lithography simulation technique for reproducing experimental data by calculation becomes very important.
There will be described one example of a lithography simulation method in a conventional technology. First, an optical image (latent image) on predetermined exposure conditions is calculated from a given mask pattern. A Gaussian function with respect to the optical image (latent image) or a multi Gaussian function obtained by weighting several Gaussian functions is subjected to convolutionary integration to thereby form a modulated optical image, and there is defined, as a dimension, a distance between two intersections of an exposure amount distribution curve of the modulated optical image and a reference intensity line for specifying a position of an edge of the pattern. The calculation of the optical image can be determined from the exposure wavelength (λ) of the exposure apparatus, the lens numerical aperture (NA), an illuminative shape, a lens aberration, a focus and the like. The convolutionary integration of the optical image with the Gaussian function means that there is represented, in a simulating manner, a dimensional fluctuation attributable to diffusion of acid of chemically amplitude resist applied onto the wafer. In this manner, in the above conventional technology, the dimension of the pattern to be formed on the wafer can be defined by a parameter of optical calculation determined by the exposure apparatus, the convolutionary integration of the Gaussian function obtained by simulating a resist process, and calculating of the intersection between the reference intensity line and the exposure amount distribution curve of the modulated optical image.
However, in recent years, a dissolution speed of the resist changes with a size of the pattern, a space width between the pattern and an adjacent pattern, magnitude of emitted light intensity and the like, and a dimensional fluctuation due to these influences cannot be predicated correctly by the conventional technique. A dimensional fluctuation due to flare (fog light) of the exposure apparatus cannot be considered completely by the above conventional technique. Since it takes very enormous calculation time to represent such phenomenon by a strict physical model, the technique is not realistic. To solve the problem, heretofore, the distance between the intersections of the reference intensity line of a predetermined intensity position and the exposure amount distribution curve of the optical image has uniformly been defined as the pattern dimension, but several methods have been proposed in which the intensity position of the reference intensity line or the exposure amount distribution curve of the optical image is shifted vertically (light intensity direction) to thereby simply take in the above phenomenon and enhance an estimation precision. These techniques include: a technique of specifying the intensity position where the intensity becomes maximum or minimum in the optical image in the vicinity of the pattern, and determining a shift amount of the optical image in accordance with the maximum or minimum intensity; and a technique of calculating a tilt of the optical image, and determining a shift amount of the optical image in accordance with the tilt. These techniques have an effect of raising a calculation precision with respect to a simple line and space pattern, but such effect cannot necessarily be recognized in many complicated shape patterns existing in actual device patterns. In the pattern having the complicated shape, the shape of the optical image of the pattern is also very complicated. Therefore, it is very difficult to correctly define the maximum or minimum intensity or the tilt of the optical image as in the above method. In a case where the shift amount of the optical image is determined by the light intensity which simply becomes maximum or minimum, or the only tilt of the optical image with respect to the pattern having such complicated optical image, a situation has sometimes occurred in which the calculation precision is deteriorated as compared with the previous technique.